1. Field
The present invention relates to an electric power steering apparatus which includes a torque detecting device for detecting a torque applied to a steering member, controlling means for outputting a control amount in response to the torque detected by the torque detecting device while having a dead zone of the torque where the control amount is not outputted, and an electric motor arranged to be controllably driven in response to the control amount outputted from the controlling means for assisting the steering action.
2. Description of Related Art
An electric power steering apparatus installed in a vehicle is designed for assisting the steering action of the vehicle with the help of an electric motor and includes, in a steering mechanism having a steering member and a steering shaft joined together, a torque sensor for detecting the torque of the steering action received by the steering member and an electric motor for assisting the steering action of the steering mechanism, whereby the electric motor can be driven in response to the steering torque detected by the torque sensor for generating a force of assisting the steering action to ease the steering force on the steering member. Also, the force of assisting the steering action can be determined in relation to the speed of the vehicle so that the steering force on the steering member is not too small during the running at high speeds of the vehicle.
Disclosed in Japanese Patent Application Laid-Open No. 2002-249061 is a current controller unit in an electric power steering apparatus which comprises a first current controller for outputting a first control signal corresponding to a difference between the target current and the present current in the electric motor, an external interference voltage estimator for estimating from the target voltage signal and the present current an external interference voltage induced on the electric motor, a second current controller for outputting a second control signal in response to an output of the external interference voltage estimator, and adding means for summing the output of the first current controller and the output of the second current controller to output the target voltage signal. The external interference voltage estimator includes a highpass filter of second or higher order provided at least at either the input side or the output side.
Disclosed in Japanese Patent No. 2838053 (U.S. Pat. No. 5,473,231 and 5,504,403) is a controller unit in an electric assist steering system which includes mixture filtering means which comprises first filter means for having a first function characteristic at a torque frequency smaller than the mixture frequency and second filter means for having a second function characteristic at a torque frequency larger than the mixture frequency, the first filter means and the second filter means being connected in parallel to each other for providing a torque signal mixed and filtered by the first and second filter means, and controlling means operationally connected to the mixture filtering means for providing a control signal to steering assisting means in response to the torque signal mixed and filtered by the mixture filtering means, whereby the torque signal is filtered by the mixture filtering means to maintain its selectable system frequency range during the operation of the system.